Coating method with precure and apparatus therefor

ABSTRACT

An apparatus and method are provided for producing a coating of heat fusible resinous material upon only a portion of a workpiece. The resinous material is deposited upon the workpiece as electrostatically charged particles. One zone of the workpiece is heated to cause fusion and cohesion of the particles while a second zone is simultaneously cooled to prevent such a result and to thereby facilitate removal of particles from the cooled zone. The apparatus and method are particularly adapted for producing thermoplastic coatings upon armature rotors for electric motors.

United States Patent [1 1 Goodridge et al.

[4 1 Aug. 26, 1975 1 1 COATING METHOD WITH PRECURE AND APPARATUSTHEREFOR [75] Inventors: William C. Goodridge, West Haven;

Donald J. Gillette; William P. English, both of Bridgeport; G. MarkMinckler, Guilford, all of Conn.

[73] Assignee: Electrostatic Equipment Corporation, New Haven, Conn.

22 Filed: Feb. 14, 1974 21 Appl. No.: 442,437

Related US. Application Data [62] Division of Ser. No. 256,499, May 24,1972, Pat. No.

[52] .U.S. Cl. 118/630; 118/239; 118/75 [58] Field of Search 118/63,106, 75, 109, 107, 118/622, 629, 630, 634, 641, 642, 643, 239,

DIG. 5, DIG. 7; 117/175; 432/137 [56] References Cited UNITED STATESPATENTS 1,856,757 5/1932 Goad 118/107 X 2,716,620 8/1955 Green 118/75 X2,900,954 8/1959 Freeze 1 18/239 3,310,431 3/1967 Loose 118/107 X3,695,909 10/1972 Fabre l17/17.5

Primary Examiner-Nile C. Byers, Jr.

[57] ABSTRACT An apparatus and method are provided for producing acoating of heat fusible resinous material upon only a portion of aworkpiece. The resinous material is deposited upon the workpiece aselectrostatically charged particles. One zone of the workpiece is heatedto cause fusion and cohesion of the particles while a second zone issimultaneously cooled to prevent such a result and to thereby facilitateremoval of particles from the cooled zone. The apparatus and method areparticularly adapted for producing thermoplastic coatings upon armaturerotors for electric motors.

r 14 Claims, 17 Drawing Figures PAIENTEB mczsms SHEET 3 BF 7PATENTEDAUGZBIHYS 3,901,185

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COATING METHOD WITH PRECURE AND APPARATUS THEREFOR This is a divisionalof application Ser. No. 256,499, filed May 24, 1972, now U.S. Pat. No.3,865,610.

BACKGROUND OF THE INVENTION Of the various ways in which coatings ofheat fusible resinous materials are produced upon various workpieces,those in which the material is applied in particulate or powdered formare often found to be the most effective and satisfactory. Suchtechniques are used to produce coatings upon a wide variety ofworkpieces, including continuous lengths of wire and strip stock as wellas individual objects which are often of a complex configuration, aswould make coating by other techniques difficult or impossible. Forexample, attempts have been made to insulate the slots of rotors andstators for electric motors by depositing the resin in powdered form,which has proven particularly difficult due to the presence of reentrantsurfaces which must be covered.

A common method of producing coatings of thermoplastic particulatematerials is to utilize heat from the workpiece to cause softening andfusion of the particles upon contact. Thus, it has long been thepractice to heat the article and to then submerge it in a bed (desirablyfluidized) of the particulate material so as to pro duce a coating uponall exposed surfaces, and as far as is known prior attempts to producecoatings from powdered resins upon electric motor components haveemployed this technique. However, the inherent drawbacks are quiteapparent, and include the need for masking of portions of the workpiecewhich are to re main free from the coating material and/or the need tohandle or direct the resin in such a manner that contact will beavoided. Not only are such precautions timeconsuming, but frequentlythey are difficult if not impossible to achieve in practice. Moreover,since the amount of material deposited using such a method is dependentupon the intensity of heat available from the workpiece and/or theduration of exposure, uniform thicknesses are oftentimes most difficultto obtain.

It is also well known that electrostatic forces may be utilized to causeattraction and adhesion of particles of thermoplastic materials to awide range of workpieces, which may thereafter be heated to melt theresin and produce the final unified coating. This approach has manyadvantages including uniformity of coverage, ease of access to undercutor reentrant surfaces, coating thickness control, etc. Nevertheless, theproduction of preferential deposits upon selected areas of the objecthas typically relied upon the use .of mechanical or air maskingtechniques which are not entirely satisfactory under certaincircumstances, such as when it is necessary to obtain a virtually cleansurface closely adjacent to one that is to be relatively thicklycovered.

Accordingly, it is an object of the present invention to provide a novelmethod and apparatus for the production of a unified, adherent coatingof a heat fusible resin upon a limited portion of a workpiece.

A more specific object of the invention is to provide such a method andapparatus for electrostatically coating the workpiece and for effectingthe removal of the resinous material from selected portions thereofwhich are to be uncoated.

An even more specific object is to provide such a method and apparatuswhereby a generally cylindrical article having reentrant surfaceportions may be coated with an adherent deposit upon the reentrantsurface portions thereof.

Another object of the invention is to provide such a method andapparatus whereby such coatings may be produced quickly, easily andeconomically, which method and apparatus may be automatic andcontinuous.

A further object is to provide a novel precuring device which is adaptedto set the coating at one zone of a workpiece while simultaneouslymaintaining the particulate form of the resin at a second zone tofacilitate its complete removal therefrom.

SUMMARY OF THE DISCLOSURE It has now been found that the foregoing andrelated objects of the invention are readily attained in an apparatuscomprising, in combination, a chassis, means on the chassis forproducing a cloud of electrostatically charged solid particles ofresinous-material, a precuring unit on the chassis, and means forcarrying the workpiece along a travel path through the cloud-producingmeans and precuring unit. The precuring unit includes means for heatinga first zone of a workpiece to be coated, and means for simultaneouslycooling a second zone thereof, the zones of the workpiece being in heatconductive contact with one another. The heating and cooling means areso disposed as to enable heating of the first zone of the workpiece to arelatively high temperature above ambient while the second zone thereofis simultaneously maintained at a relatively low temperaturesubstantially below the relatively high temperature. Exposure of theworkpiece to the charged particles fromthe cloud-producing means, withthe workpiece charged effectively opposite to the particles, causes alayer of particles to deposit thereon. In the precuring unit, theheating means at least partially fuses and coheres the particles at thefirst zone of the workpiece and the cooling means substantially preventsfusion and coherence of particles at the second zone thereof, removal ofthe particles from the second zone thereby being facilitated.

In preferred embodiments of the invention, the heating and cooling meansof the precuring unit extend along substantially the same length of thetravel path, and the cooling means comprises an element having a cooledsupport surface upon which the second zone of the workpiece rests inheat transfer contact during movement through the unit. The coolingmeans may additionally include an overlying element having a cooledlower surface extending substantially parallel to and in spacedalignment over the support surface to provide a convective coolingeffect upon the second zone of the workpiece during passagetherebeneath. In such a case, the conveyor may include an upstandingelement for supporting the article with the first and second zones ofthe article lying on opposite sides thereof, and the conveyor elementmay cooperate with the underlying element of the cooling means toprovide a shield against heat flow by radiation and convection to thesecond zone of the article.

The apparatus preferably includes cleaning means positioned on thechassis along the travel path downstream of the precuring unit foreffecting the removal of particles of resinous material from the secondzone of the workpiece. Most desirably, it also includes post heatingmeans positioned along the travel path downstream of the cleaning means.The post heating means is adapted to fully heat the workpiece so as tounify and produce from the remaining particles of resinous material anadherent coating on the first zone thereof.

The apparatus may be particularly adapted for producing a coating upon agenerally cylindrical article having a central portion providing thefirst zone thereof and end portions extending axially from either sideof the central portion together providing the second zone of thearticle. In such an instance, the cooling means of the precuring unitdesirably comprises two elements, each having a cooled surface extendingalong an opposite side of the travel path and being adapted to supportand cool one of the end portions of the article during movement thereofalong the travel path through the unit. The heating means thereof maycomprise a heating element extending along the travel path and lyinggenerally between the cooled surfaces to heat the central portion of thearticle during movement through the unit.

The precuring unit may include a base providing at least in part thecooling means thereof. The base may have an elongated channel extendingtherein along the travel path through which at least the lower portionof the conveyor passes, the surfaces of the base defining the channelbeing cooled to provide a cooling effect thereabout. Preferably, theheating means employed comprises a heating element supported by a covermember which is moveably mounted upon the chassis for displacement froma normal position over the travel path to a position outwardlytherefrom. When the cooling means includes an overlying element having acooled lower surface, such an element may be supported by the covermember and disposed as hereinbefore described when the cover member isin closed position.

In especially preferred embodiments of the invention the cloud producingmeans employed in the apparatus includes an electrostatic cloud chamber.Such a chamber may comprise a receptacle having means for producing afluidized bed of charged particles including a gas-permeable plateextending thereacross in a generally horizontal intermediate plane andspaced above the bottom wall of the receptacle to define a plenumchamber therebelow. The receptacle also has electrode means extendingthereacross to electrostatically charge particles of solid resinousmaterial passing proximate thereto. Most desirably, the apparatus willinclude a particulate material reservoir having feed means communicatingwith the cloud chamber. In such a case, the electrode means may span alesser area than the gaspermeable plate to provide an electrode-freevertical corridor within the receptacle through which particles of theresinous material may pass without acquiring a significant charge. Adevice for sensing the level of the bed of particles within thereceptacle, in response to which the feed means conveys resinousmaterial from the reservoir to the chamber when the bed level fallsbelow a preselected height, may also be provided. The sensing device ispositioned within the vertical corridor over the horizontal porousplate, to thereby minimize the effect of electrostatic charging upon thesensed level of the bed. The electrode employed may be a generallyplanar, grid-like structure disposed adjacent the upper surface of thegas-permeable plate, and electrode and plate may be substantiallycoextensive except at one area of the plate over which the electrodedoes not extend, thereby providing the electrode-free vertical corridor.

Certain objects of the invention may be attained by the provision of aprecuring unit adapted for heating the cylindrical core portion of anelectric motor annature rotor while simultaneously cooling the axiallyextending shaft portions thereof during passage through the unit. Theunit comprises a base having an elongated, upwardly opening channelextending therein with generally horizontal upper surfaces of the baseextending along each side of the channel, means being provided forcooling such surfaces to conductively cool shaft portions restingthereon. The channel is dimensioned and configured to receive the coreportion oi the rotor suspended therewithin with the shaft portionsthereof resting upon the upper surfaces. The precuring unit alsoincludes an elongated heating element which is normally axially alignedover the channel and is disposed to heat the core portion during passagethrough the channel.

Additional objects are attained in accordance with the method of theinvention in which a unified, adherent coating of heat-fusible materialis produced upon only a portion of a workpiece having proximate firstand second zones in heat conductive contact with one another. The methodinvolves producing a cloud of electrostatically charged solid particlesof resinous material and exposing the workpiece to the charged particleswith the workpiece charged effectively opposite thereto to cause a layerof the particles to deposit over the first and second zones thereof. Thefirst zone of the workpiece is heated to a relatively high temperatureabove ambient while the second zone is simultaneously cooled. As aresult, the particles on the first zone of the workpiece are at leastpartially fused and cohered while fusion and coherence of particles onthe second zone are substantially prevented due to the relatively lowtemperature maintained thereat, which is substantially below therelatively high temperature of the first zone. Thereafter, particles ofresinous material remaining on the second zone of the workpiece areremoved.

Subsequent to the simultaneous heating and cooling step, the method willgenerally include the step of heating the workpiece to at least aboutthe melting point of the resinous material to unify the particlesthereof and to produce an adherent coating upon the first zone of theworkpiece. In addition, it may include the step, ef fected prior to thesimultaneous heating and cooling step, of removing a portion of thelayer of particles deposited upon the first zone of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of apparatusembodying the present invention;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a side elevational view of the coating process unit of theapparatus of FIGS. 1 and 2, drawn to an enlarged scale and with housingportions removed to expose internal features thereof;

FIG. 4 is a perspective view of an armature rotor for which theillustrated apparatus is particularly adapted;

FIG. 5 is a fragmentary perspective view of the forward end of thecoating process unit including the load zone and a portion of theelectrostatic coating station, drawn to a scale enlarged from that ofFIG. 3;

FIG. 6 is an enlarged sectional view along line 6-6 of FIG. 3illustrating the support and positional control structure provided atthe load zone and showing an armature rotor carried on the forwardconveyor for movement therethrough;

FIG. 7 is an end view of the electrostatic coating station along line 77in FIG. 3 with portions of the housings broken away to illustrate theinternal features thereof and drawn to a greatly enlarged scale;

FIG. 8 is a side elevational view of the sensing device employed in thecloud-coating unit of the electrostatic coating station;

FIG. 9 is a fragmentary end view along line 9-9 in FIG. 3 showing thepowder removal zone of the apparatus with the contact belt unit thereofin its normal operating position, drawn to a greatly enlarged scale andhaving portions in vertical section to illustrate the constructionthereof;

FIG. 10 is a front view of the powder removal zone at an acute angle tothe upper surface of the deck, drawn to a slightly diminished scale fromthat of FIG. 9 and showing the contact belt unit in its raised positron;

FIG. 11 is a fragmentary end view of the powder removal zone along linellll of FIG. 3, drawn to the scale of FIG. 9;

FIG. 12 is a fragmentary plan view of the shaft cleaning units providedwithin the powder removal zone, drawn to a scale enlarged from that ofFIG. 10 and with the hold-down brackets removed to expose the vacuumslots thereof;

FIG. 13 is a side elevational view of the vacuum nozzle and associatedparts employed with each of the units of FIG. 12;

FIG. 14 is an enlarged sectional view along line 14-14 in FIG. 3 showingthe precuring unit of the apparatus with an armature rotor passingtherethrough, and in phantom line showing the raised position of thecover assembly;

FIG. 15 is a perspective view of the air knife assembly at the powderrecovery zone of FIG. 3, drawn to a greatly enlarged scale;

FIG. 16 is a fragmentary perspective view to a greatly enlarged scale ofthe intermediate conveyor employed in the apparatus; and

FIG. 17 is a fragmentary perspective view of one band of the endmostconveyor of the apparatus, drawn to the scale of FIG. 16.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Turning now in detailto the appehded drawings, therein illustrated is an armatureslot-coating system embodying the present invention and details of thevarious units and zones thereof. FIGS. 1 and 2 illustrate the overalllayout of the system, the heart of which is the coating process unit, sodesignated on the drawing. Auxiliary to the coating process unit is anoven and a cooling unit, and main control and oven control facilitiesare furnished. Also included in the system to enable a desirable mode ofoperation is a power recovery and feed unit and a powder replenishmentunit. As will be appreciated from FIG. 2, the workpieces are loaded atan infeed zone at the left-hand end of the coating process unit fromwhich they pass serially through an electrostatic coating zone, a powderremoval zone, a precure zone. and a powder recovery zone; they then passinto the oven and finally through the cooling unit. Excess powder fromthe electrostatic coating zone is recovered in the powder recovery andfeed unit and is returned through an appropriate conduit to the coatingunit on a substantially continuous basis, and additional powder isfurnished from the powder replenishing unit as needed. An electricinterface access channel runs along the rear of the coating process unitto provide at the various zones thereof.

With specific reference now to FIG. 3, the coating process unit of thesystem is depicted in greater detail. It includes a frame 10 on whichare rotatably supported three conveyor drive sprockets, generallydesignated by the numerals ll, 12 and 13 respectively from left to rightin the Figure, and idler wheels 14 are positioned between adjacentsprockets. A forward endless conveyor, generally designated by thenumeral 16, runs about sprockets 11 and 12 and the idler wheel 14therebetweeen; a center endless conveyor, which is generally designated18, runs about sprockets 12 and 13 and about the idler wheel 14positioned between them, and a rearward endless conveyor, which isgenerally designated 20 and is fragmentarily illustrated, runs about theright-hand sprocket l3 and a cooperating sprocket which is notillustrated and is positioned adjacent the end of the cooling unit shownin FIGS. 1 and 2. A drive pulley 22 operates the powder removal unit andis driven by the electric motor 24 which is supported within the frame10. A second motor 25 is connected to sprocket 13, thereby synchronouslydriving all conveyors l6, 18, 20 since they are coupled by thesprockets, ll, 12, 13.

Although the invention is not to be construed as limited to coating ofany particular workpiece, and may be feasible for coating selectedportions of objects which are elongated or 0 continuous length, thesystem illustrated is especially suited for the coating of armaturerotors of the type generally designated by the numeral 26 in FIG. 4, andis intended principally for that purpose. The rotor 26 is ofconventional configuration and includes a cylindrical core portion 28having spaced about its circumference four axially extending, reentrantwinding slots 30. Extending from opposite ends of the core portion 28are simple and crank-type shafts 32, 34 respectively, and the shaft 34has a spring clip 35 engaged upon it adjacent the end of the coreportion 28.

As will be appreciated, the slots 30 of the rotor 26 are designed toreceive wire windings, making it necessary to provide the slots 30 andthe opposite end faces 37 of the core portion 28 with a layer ofinsulating material to enable magnetic poles to be defined thereon. Itis also important that the outer circumferential surface of the coreportion 28 and the shafts 32, 34 be free from insulating material; thepresent system is unique in enabling the rapid and facile production ofcoated rotors having deposits of insulating material which are presentonly at selected locations and are of substantially uniform thickness.

FIG. 5 illustrates in greater detail the loading zone of the coatingprocess unit, whereat a narrow rectangular opening 38 is providedthrough the deck 36 of the frame 10 to accommodate the edge of drivesprocket 11. As can be seen, the forward conveyor 16 is comprised of twoindependent flexible and continuous parallel bands, generally designatedby the numerals 44 and 45, and the drive sprocket 11 consists of a pairof parallel sprocket wheels mounted on a common shaft for concurrentrotation. Each of the sprocket wheels 40 has about its circumferentialedge of multiplicity of small rectangular teeth 42; the belt portion 46of each of the bands 44, is provided with a multiplicity of rectangularapertures 48 which are spaced along the length thereof, the apertures 48meshing with the rectangular teeth 42 of the respective sprocket wheels40 as the bands pass thereover along their travel path. Extending at aright angle from the inner edge of the Belt portion 46 of each of thebands 44, 45 are a multiplicity of carrier tabs 50, 50' respectively,and each tab 50, 50 has bevelled shoulders 51 leading into the shaftslots 52, 52 therebetween. As will be appreciated, the slots 52, 52' aredimensioned to receive the shafts of the armature rotor 26, and the tabs50 are slightly narrower than the tabs 50 to render the slots 52somewhat wider than the slots 52, thereby enabling close-fittingengagement of shafts 32, 34, notwithstanding their different diameters.It will be evident that the bevelled shoulders 51 facilitate insertionand removal of the shafts of the armature rotors 26 into and from theslots 52.

As can most readily be seen by additional reference to FIG. 6, one of apair of elongated rectangular curb blocks 54 extends along each side ofthe upper flight of the conveyor 16, with the curb blocks 54 beingsecured to the deck 36 by bolts 56 (fastened in an appropriate manner,not illustrated). Coextensive with each of the curb blocks 54 is a guiderail 58 which is secured upon the upper surface of the associated curbblock 54 by a number of bolts 60 spaced along the length thereof. Ashallow recess 61 is provided along the upper surface adjacent the inneredge of each of the curb blocks 54 enabling the belt portion 46 of theconveyor bands 44-, 45 to pass between the curb blocks 54 and the bottomsurface of the guide rails 58. The guide rails 58 have inner surfaceswhich extend downwardly and then at an angle inwardly to provide guidesurfaces 62 sloping downwardly toward the travel path. The guidesurfaces 62 define therebetween a trough which is dimensioned so thatarmature rotors 26 carried by the conveyor 16 extend thereacross withlittle free space adjacent the ends, thus ensuring that the rotors 26remain accurately positioned across the conveyor 16 and centrallypositioned on the axis of the travel path of the unit.

Extending forwardly from adjacent the ends of the curb blocks 54- is asupport extension 66 which underlies the conveyor 16 and providessupport therefor as the bands 44, 45 disengage from the sprocket wheels40. Supported above the extension 64 is a loading platform portion 66from which extend rearwardly a pair of thin support rails 68 which aresecured in a parallel relationship against the inner faces of the curbblocks 54. The loading platform 66 is provided to facilitate loading andseating of the rotors 26 in the slots 52 of the conveyor 16, and thesupport rails 68 provide underlying support for the shafts 32, 34 as therotors 26 proceed along the travel path, it being appreciated that theshafts ride upon the upper edges of the support rails 68 rather thanresting at the bottom of the slots 52. As a result, the conveyor 16serves only to drive the rotors 26 forwardly through the system, withcontact upon the rails 68 causing them to rotate as they are conveyed.

From the load zone, the armature rotors 26 are conveyed to theelectrostatic coating station illustrated in detail in FIG. 7, which iscomprised of a hood, a powder feed stack, and an electrostatic coatingchamber, generally designated by the numerals 72, 74 and 76respectively. The electrostatic coating chamber 76 consists of anupwardly opening enclosure 78 secured against the bottom surface of thedeck 36 and having a bottom wall opening through which air is chargedfrom a pressurized source 79 thereof. A horizontal porous ceramicpartition 80 divides the enclosure 78 into a lower air plenum chamber 82and an upper cloud chamber 84. The partition 80 supports an overlyinggrid-type electrode 86 connected to a diagrammatically illustrated highvoltage source 88 and extending partially across the enclosure 78 toprovide an electrodefree area between its inner edge 87 and the sidewall89, through which extends an imaginary vertical corridor.

Within the corridor, supported upon the depending bracket 92, is apneumatically operated fluidic sensing device comprised (as seen in FIG.8) of a body 90 with a wire actuating finger 94 extending therefrom; oneappropriate device is sold by Norgren Fluidics of Littleton, Coloradounder the name FEATHERFLEX SFS- 010-000. On the outer end of the wirefinger 94 is a float sphere 96 which may be fabricated of a foamedpolystyrene or comparable lightweight material, and pneumatic controllines 98 extend from the body 90 and are connected to control means (notillustrated).

The feed stack 74 consists of a sifter box 100 having a screen 102horizontally positioned across the central portion thereof and having arecycle feed conduit 104 and a replenish conduit 106 leading thereinto.As will be appreciated, the conduit 104 extends from the pow derrecovery and feed unit and the conduit 106 extends from the powderreplenishment unit, both shown in FIGS. 1 and 2. The conduits 104, 106deliver thermoplastic resin powder 103 into the upper portion of thesifter box 100 from which it passes through the screen 102 and theopening 108 in the deck 36 with lumps and foreign matter being removedby the screen 102. The powder 103 then falls upon the porous partition80 where it becomes fluidized by air passing upwardly from the plenumchamber 82 in a conventional manner. The fluidized powder 103 exerts anupward force upon the float sphere 96 of the fluidic sensing device;when the quantity of powder 103 above the partition 80 is insufficientto urge the sphere 96 (and hence the actuating finger 94) upwardly tothe necessary extent, a signal from the sensor causes the control means(not illustrated) to deliver an additional quantity of powder 103through the conduit 106 from the powder replenish unit, therebycorrecting the deficiency.

The hood 72 is positioned over an elongated slot 110 in the deck 36along which the parallel guide rails 68 extend. It is secured to thedeck by bolts 112 and has a tunnel portion 114 with an end wall 116forming a partial closure therefor and defining a tunnel opening at eachend thereof. A stack portion 118 extends upwardly from the tunnelportion 114 of the hood 72, and has a takeoff conduit 120 which isattached to a suitable vacuum source and enables excess powder to beremoved from the coating station. Such powder is returned to therecovery and feed unit for ultimate recycle through the conduit 104leading to the feed stack 74. An elongated baffle plate 122 is inclineddownwardly from each sidewall of the tunnel portion 114 toward thetravel path of the unit, and the plates 122 cooperate with the carriertabs 50, 50 to confine powder 103 which passes upwardly through the slot110 to the central portion of the rotors 26 passing thereover.

As will be appreciated, the powder 103 employed for the coatingoperation is of such a nature that it is capable of acquiring anelectrostatic charge as the particles pass through the grid electrode86. The rotors 26 are maintained at ground potential (such as bygrounding the conveyor 17 with which they are in contact) during passageover the slot 110, thus causing attraction and adherence of chargedpowder particles to the surfaces of the rotors 26, with theelectrostatic effect ensuring that all exposed surfaces, includingwinding slots 30, are coated. Due to the charge on the powder particles,it is important that the fluidic sensing device be positioned over theelectrode-free area 85 of the horizontal partition 80. In this regioncharging of particles is minimized, as a result of which the attractiveforce from the grounded rotors 26 is quite insignificant and particlesthereat are elevated only by the buoyant effect of the pressurized air.Otherwise, the electrostatic force on the particles would lead to aninaccurate indication of the quantity of powder present in the system,rendering control of the automatic replenishment system virtuallyineffective.

Since the armature rotors 26 must be substantially free of insulatingmaterial on the circumferential surface of the core portion 28 and alongthe shafts 32, 34, and since in the coating step powder deposits uponall exposed surfaces, the method and apparatus of the invention requirethat means be provided for removing powder from selected surfaces of therotor where it is unwanted. To that end, the illustrated apparatus isprovided with a powder removal station which includes the contact beltunit, generally designated by the numeral 124, and shown in FIGS. 3, 9and 10. The contact belt unit 124 includes an elongated forward framemember 126 from which extend rearwardly triangular mounting brackets 128which are pivotally supported upon posts 130 projecting upwardly fromthe deck 36. In this manner, the units 124 is hingedly supported forready displacement from the position over the deck 36 shown in FIG. 9 toits open position in FIG. 10. Affixed in a central location behind theforward frame member 126 is a pinion block 131 which, in turn, has agear train block 132 mounted behind it. A short central shaft 134 isjoumaled at its ends by appropriate means to extend transversely throughthe forward frame member 126, the pinion block 131, and the gear trainblock 132, and it has a drive gear 136 affixed on it within the geartrain block 132. The shaft 134 also has a drive pinion 138 affixed to itin front of the gear 136, with the pinion 138 residing generally withinthe pinion block 131. A lower shaft 140 is joumaled at its ends andextends transversely between the pinion block 131 and the gear trainblock 132; on it is affixed, in meshing engagement with the drive gear136, an upper transfer gear 142. The transfer gear 142 communicatesthrough a deck opening 143 with a lower transfer gear 144 which issupported upon a shaft 146 positioned and appropriately joumaled (bymeans not shown) below the deck 36. As can be seen in FIG. 3, the lowertransfer gear 144 meshingly engages a gear 148 which is affixed to theshaft on which the drive pulley 22 is supported. In this manner, poweris delivered from the motor 24 through the drive pulley 22 and the trainof gears 148, 144, 142 ultimately to the drive gear 136 for the contactbelt unit 124. As can be seen, pivoting the unit 124 upwardly about theposts simply disengages the gears 142 and 144, discontinuing operationof the unit 124 and permitting access to the normally covered portionthereunder.

A belt pulley shaft 150 is joumaled in the forward frame member 126 andpinion block 131 on either side of the central shaft 134, and a pulleypinion (not exposed but identical to pulley pinions 152 to be discussedhereinafter) is affixed to the inner end of each of the shafts 150 andis in meshing engagement with the drive pinion 138. (It will beunderstood that the pulley pinion on shaft 150 to the left of shaft 134in FIG. 10 lies behind pinion 138, as viewed in FIG. 9, and that thepulleys and belt assembly at the left side of FIG. 9 are shown along asection line somewhat forward of line 9--9.) To the opposite ends of thepulley shafts 150 are affixed belt pulleys 154. Spaced to either side ofthe central pinion block 131 is an auxiliary pinion block 156 in whichis contained a pair of belt pulley shafts 150 and a transfer pinionshaft 134 therebetween. The inner ends of the pulley shafts 150 haveaffixed to them pulley pinions 152 (as can be seen in the left-handauxiliary pinion block 156 in FIG 10) and the transfer pinion shaft 134has affixed to its inner end a transfer pinion 158 in meshing engagementwith each of the pulley pinions 152 on either side thereof. Adjacenteach end of the forward frame member 126 is a rectangular bearing block162 in which is journaled, by appropriate means, a belt pulley shaft150. A belt pulley 154 of the type previously referred to is secured onthe outer end of each belt pulley shaft supported in either theauxiliary pinion blocks 156 or the bearing blocks 162.

The eight pulleys 154 function as four sets with adjacent pairs ofpulleys supporting a belt assembly consisting of an underlying supportdement 164 and an outwardly exposed contact element 166. The contactelement is of foamed polyurethene or a comparable material providing acellular outer surface. Such a structure enables the contact element 166to pick up powder from the surface of the core portion 28 simply bycontact therewith, with no wiping or brushing action being necessary ordesirable. The support element 164 may be a timing belt (i.e., havingtransversely extending ridges about its inner surface) with the pulleys154 being provided with corresponding ridges and grooves, or squareteeth, to cooperate therewith. Drive power is transferred from the motor24, through the gears 148, 144, 142, 136, to the pinion 138 within thecentral pinion block 131, and to the innermost belt pulleys 154. Due tothe interconnection through the pulley pinions 152 and transfer pinion158 within each of the auxiliary pinion blocks 156, the belt assemblieson the outer sets of pulleys 154 are simultaneously driven, with allbelt assemblies rotating at precisely the same rate and in the samedirection.

As is seen in F IG. 9, a central sprocket wheel 40 having rectangularcircumferential teeth 42 is supported on a common shaft (not shown) withtwo outside sprocket wheels 40. The outside wheels 40 correspond to thesprocket wheels bearing the same numeral which constitute drive sprocket11, and the three commonly supported wheels 40, 40' provide theintermediate drive sprocket l2. Endless conveyor 18 has the constructionillustrated in FIG. 16 and passes about the central sprocket wheel 40'.The conveyor 18 consists of a central band 176 having carrier tabs 178,178' extending at right angles from the side margins thereof.

The tabs 178' are slightly narrower than the tabs 178, again to renderthe slots 180' therebetween slightly wider than the slots 180 betweenthe tabs 178 to snugly receive the shafts 34, 32 of the rotor 26,respectively. The following edges of each of the tabs 178, 178' havebevelled shoulders 51 to facilitate entry of the shafts 32, 34thereinto; however, it will be noted that the forward edges of the tabs178, 178' are not bevelled, and the reason therefor will be explaineddirectly.

As can be seen in FIG. a transfer of the rotors 26 occurs within thepowder removal zone with the rotors 26 shifting from the forwardconveyor 16 to the intermediate conveyor 18. Engagement of bothconveyors 16, 18 on different sprocket wheels 40, 40 of the common drivesprocket l2 and the construction employed permits conveyor 18 to passbetween the bands 44, 45 of the conveyor 16. At the point of commontangency of the conveyors 16, 18 to sprocket 12 the respective slots 52,180 thereof are substantially aligned, causing the shafts 32, 34 of therotors 26 to momentarily reside in slots of both conveyorssimultaneously. As the bands 44, 45 of the forward conveyor 16 passdownwardly about the sprocket 12, the upper corners of the tabs 180,180' of the intermediate conveyor 18 engage behind the shafts 32, 34 tosmoothly and effectively carry them out of the slots 52 with thebevelled shoulders 51 at the following edges of the tabs 50, 50'facilitating withdrawal. Thereafter, the rotors 26 are propelled throughthe system by the center conveyor 18.

Assuming movement to be in a left to right direction, contact of theends of the shafts 32, 34 upon the support rails 68 causes rotation ofthe rotors 26 in a clockwise direction. If the motor 25 also drives thebelt assemblies of the contact belt unit 124 in a clockwise direction,the direction of rotation of the rotors 26 will reverse uponencountering the lower flight of element 166 at the entrance of the unit124 (the relationship at contact being as depicted in FIG. 9). Suchcontact causes a significant proportion of the powder on the outercircumferential surface of the cylindrical core portion 28 of the rotors26 to be displaced therefrom and to fall into the powder recovery hopper184, which is positioned at an appropriate location beneath the deck (asmay be seen in FIG. 3). The hopper 184 is connected to the powderrecovery and feed unit through a vacuum system (not illustrated) by aconduit 186. Most of the remaining powder on the surface of the coreportion 28 is picked up by the contact element 166 of the belt assembly,as previously described, with any additional powder being removed by thesuccessive belt cleaning effects in the same manner. As will beappreciated, since the rotors 26 are supported for free rotation, aftercontact with the contact element 166 they turn at precisely the samespeed under the influence thereof. This prevents relative wiping orbrushing action between the element 166 and the rotors 26, such as wouldtend to cause uneven deposits to be produced at the edges of the slots30. The nozzles 1'70 and associated vacuum conduits 172 are adjustablysupported in the bifurcated end portions of the nozzle support arms 168with the nozzles 170 lying closely adjacent the contact elements 166. Inthis way, the powder picked up by the elements 166 is withdrawn from thecells thereof and is conveyed to the recovery portions of the system forrecycle.

Positioned within the powder removal zone near the forward end of thesecond belt assembly of the unit 124 is a pair of vacuum blocks 188,which are secured to the deck 36 along the sides of the travel path. Ascan best be seen in FIG. 12, each of these blocks has a face plate 190,190' secured upon its upper surface and of an elongated vacuum channel192 extending lengthwise therein. As can be seen with additionalreference to FIGS. 3 and 13, a vacuum nozzle 194 of generally oval crosssection is secured against the lower surface of each of the vacuumblocks 188, each nozzle 194 having a circular throat portion 196 aboutwhich is positioned an annular mounting collar 200 by which it issecured against the associated vacuum block 188 (by means not shown).Secured over the throat portion 196 of each nozzle 194 is a vacuum hose198 which is connected to a vacuum source (not shown) and ultimately tothe powder recovery and feed unit illustrated in FIGS. 1 and 2.

The face plates 190, 190 on the vacuum blocks 188 are provided withelongated slots 202, 202', each of which extends in a generally angularrelationship outwardly from the travel path. These slots 202, 202'register over the channels 192 in the blocks 188 and serve to define aflow passage for air under the influence of vacuum drawn throiigh theconduits 198. As the armature rotors 26 travel between the vacuum blocks188 with the shafts 32, 34 thereof in rolling contact upon the faceplates 190, 190' respectively, the vacuum effect from below thoroughlycleans the shafts 32, 34 of any powder which may have become depositedthereon. Normally, powder will be present in the shafts 32, 34 as aresult of the initial electrostatic coating operation and/or due todisplacement from the circumference of the cylindrical core portion 28during powder removal by the first belt assembly in the contact beltunit 124. The divergent disposition of the slots 202, 202' will causeparticles of powder to be removed first from the portions of the shafts32, 34 adjacent the core portion 28 and progressively outwardlytherealong. It will be appreciated that the nonlinear and nonuniformconfiguration of the slot 202' is necessitated by the configuration ofthe crank shaft 34 which passes thereover. As can be seen in FIGS. 9 and10, a hold-down bracket 201 is secured to each of the vacuum blocks 188.Each bracket 201 includes a pressure plate element 203 which overliesthe slot 202, 202' of the associated block 188 and serves to engage thetops of the shafts 32, 34 as they are conveyed thereunder, therebyforcing the shafts against the face plates 190, 190' to ensure efficientpowder removal therefrom.

After travelling past the vacuum blocks 188, the armature cores 26 areconveyed beneath the third of the series of belt-cleaning assemblieswhile being supported upon parallel side rails 182. The fourth contactbelt effect is similar in design to the first three, with the exceptionthat it is provided with contact belt assemblies for the shafts 32, 34as well as for the cylindrical core portion 28 of the rotors 26. Theconstruction of this portion of the contact belt unit 124 is mostclearly illustrated in FIG. 11, wherein it can be seen that a set ofthree belt pulleys 154 are mounted on a common shaft for simultaneousrotation. Each of the pulleys has a belt assembly consisting of asupport belt 164 and a contact belt 166 constructed as hereinbeforedescribed, and it will be appreciated that the belts extend between twoof such sets of three belt pulleys 154 (as can be seen in FIG. 10).

From the contact belt unit 124, the armature rotors 26 pass into aprecuring unit, generally designated by the numeral 204 and shown inFIGS. 3 and 14. With specific reference to the latter figure, it can beseen that the precuring unit 204 consists of a cover assembly, generallydesignated by the numeral 206, which has affixed thereto a pair of anglebrackets 208, only one of which is visible in FIG. 14. The brackets 208are secured at one end to the cover assembly 206 by appropriate bolts210, and the opposite ends thereof are pivotally supported upon posts212 which are mounted upon the deck 36 of the machine. Also secured tothe cover assembly 206 is a right angle contact arm 214 which has anelement extending over the end of a spring-loaded plunger assembly 216.In normal operation the cover assembly 206 will be maintained in theposition illustrated in full line in FIG. 14 by fluid pressure meansacting against the upward force of the plunger assembly 216. If themachine stops or if some emergency situation occurs, the fluid pressureforce is disrupted, permitting the plunger assembly 216 to immediatelyraise the cover assembly 206 to the position shown in phantom line.

The cover 218 of the cover assembly 206 is elongated (as can be seen inFIG. 3) and is of inverted, generally Ushaped configuration (as is shownin FIG. 14). It has a number of layers 220 of insulating material liningthe top wall thereof, which are secured, along with a metal sheetreflector 222 and a pair of elongated angular baffle plates 224, to thecover 218 by appropriate bolts 226. Heating elements 228, which may beCALROD units, extend longitudinally within the cover 218 and aresupported therein by a number of inserts 230, which are spaced along thelength of the cover 218 and have pairs of apertures 231 to receive andsupport the heating elements 228. The baffle plates 224 are constructedwith inclined walls 232 which slope downwardly and inwardly toward oneanother and toward the travel path; the walls serve to support theinserts 230 as well as their primary function of reflecting andconcentrating heat from the elements 228 upon the central portion of thetravel path.

Supported along each side of the cover 218 is at the lower edges thereofis one of a pair of configured cooling blocks 234, which may beconstructed of aluminum or another suitable material having a high heattransfer coefficient. It will be appreciated that these cooling blocksare elongated and extend along substantially the entire length of thecover 218. The cooling blocks 234 have inner upstanding elements 235which are configured to define behind them circular recesses 236, in

which are supported cooling tube portions 238. Small,

downwardly opening U-shaped channels 240 are defined along the lowerinner edges of the upstanding elements 235, and a depending ridge 242 isprovided on each of the cooling blocks 234 adjacent the lower outer edgethereof.

The ridges 242 of the cooling blocks 234 are received in narrow,upwardly opening U-shaped channels 244 defined in the upper surface ofthe base of the precuring unit 204, the base being generally designatedby the numeral 246. A relatively large, upwardly opening U- shapedchannel 250 extends axially in the base 246 along its entire length todefine the travel path therethrough. The underside of the base 246 has aU-shaped channel 248 of a similar size running along its length, withthe opposed relationship of the channels creating a relatively thinfloor portion 252 therebetween. A rectangular base block 254 is seatedin the downwardly opening channel 248 and is welded in place with itsupper surface spaced a short distance downwardly from the lower surfaceof the floor portion 252 to define a shallow water channel 256therebetween. Upwardly opening U-shaped slots 258 are formed in theupper surface of the block and along the entire length thereof betweenthe central channel 250 and each of the relatively narrow channels 244,and each of the slots 258 has a cover strip 260 engaged over its openend to thereby define closed conduits therewithin.

At each end (only one end being shown) the base 246 is provided with atransverse bore 262 which communicates with the opposite ends of theshallow water channel 256. To facilitate manufacture, the bores 262 aresimply drilled inwardly from the side of the base 246, with plugs 264being inserted afterward to close the ends. Extending upwardly andinwardly from the opposite ends of the bores 262 are short connectingchannels 266 (only two of the four of which are seen because only oneend of the base 246 is illustrated), one of which communicates with eachof the U-shaped slots 258 at one end thereof. Finally, an inlet port 268communicates from the lower surface of the base 246 with the transversebore 262, and it will be appreciated that the other end of the base 246has a similar port 268 communicating with the associated bore 262provided thereat.

In operation, the precure unit 204 heats the cylindrical core portion 28of each of the armature rotors 26 while simultaneously cooling theshafts 32, 34 thereof. Heat is generated by the elements 228, with thereflector 222 and the bafile plates 224 effectively directing the heatinwardly toward the core portion 28 and concentrating it thereat. Thesimultaneous cooling effect is provided by passing water through thebase 246 and the configured cooling blocks 234. With respect to the base246, water passes inwardly through illustrated port 268, transverselyacross the block in the bore 262, and thence along the length of thebase 246 within the shallow water channel 256 and the U-shaped slots 258to pass outwardly through the transverse bore and port not illustrated.In this manner, a cooling effect is transmitted through the thin floorportion 252 to cool the central band 176 of the conveyor 18 and thesurrounding area. Water passing through the slots 258 serves not only tocool the sides of the conveyor 18, but has the primary function ofproducing a cooling effect. through the cover strips 260. The shafts 32,34 of the armature rotors 26 contact these strips 260 directly, so thatthe cooling water passing therebeneath very effectively lowers thetemperature of those portions. The configured blocks 234 are cooled bywater passing into one of the cooling tube portions 23 and out of theother, the portions 238 being parts of a continuous conduit. As aresult, the horizontal part 237 of each of the blocks 234 is cooled andcooperates with the base 246 to effectively maintain the shafts 32, 34at a relatively low temperature. The upper ends of the carrier tabs 178,178' of the conveyor 18 extend into the downwardly opening U-shapedchannels 240 adjacent the lower inner edges of the blocks 234, and arecooled thereby. In addition, the engagement of the depending ridges 242in the upwardly opening channels 244 increases the effectiveness ofcooling by unifying the cover 218 and base 246 of the precure unit 204.A low temperature shell is thereby defined about the travel path throughthe precuring unit 204, except in the limited area thereabove at whichthe heating effect is concentrated. Accordingly, the unit 204 veryeffectively cools parts of the rotors 26 which lie outwardly of thecylindrical core portion 28, while the portion 28 is heated to arelatively elevated temperature. As a result, only resin on the coreportion 28 is melted and fused, with any powder remaining on the shafts32, 34 being maintained in a solid particulate state. This permitsremoval of un-- wanted powder from the shafts 32, 34 whilesimultaneously producing a relatively adherent coating in the slots ofthe core portion 28, the circumferential surface of the core portion 28having been freed from powder by the action of the belt assemblies inthe contact belt unit 124.

Turning now in detail to FIG. 15, therein illustrated is an air knifeassembly, generally designated by the numeral 270, which is positionedimmediately downstream from the precure unit 204, as can be seen in FIG.3. The air knife assembly 270 consists of a pair of spaced, invertedU-shape bridge members 272 which have mounted thereon a pair of spacedair manifold bars 274. The manifold bars 274 are adjustable (by meansnot shown) to vary their spacing and angular attitude relative to oneanother, and each of them has a number of flattened nozzles or airknives 276 extending downwardly therefrom toward the deck 36 of themachine. In general alignment under each of the manifold bars 274 is anupwardly opening elongated trough 278 which is connected to a vacuumsource (not shown) through vacuum conduits 280 attached to the lowerends thereof. As will be readily appreciated, armature rotors 26 passfrom the precuring unit 204 beneath the bridge members 272 of the airknife assembly 270 with their shafts 32, 34 extending outwardly over thetroughs 278. Air is charged under pressure into the manifold bars 274through the air conduits 282 and is blown at high velocity upon theshafts 32, 34 through the air knives 276 as the rotors 26 travel throughthe assembly 270. Due to the discrete form in which the particles aremaintained as a result from the cooling effects of the precuring unit204, the air from the knives 276 effectively dislodges any particlespresent on the shafts 32, 34 and propels them into the troughs 278. Inthis manner, the shafts are thoroughly cleaned prior to entry of therotor 26 into the oven, with the excess powder being returned to thesystem through the conduits 280.

Uncoated armature rotors 26 are loaded in successive pairs of slots 52,52 of the conveyor bands 44, 45 at the infeed station of the apparatus,and enter the oven with at least partially fused and cohered coatings ofresin in the slots 30 and on the end faces 37 thereof. Thecircumferential surfaces of the cylindrical core portions 28 of therotors 26 are virtually devoid of any powder particles. This isaccomplished by the contact belt elements 166, which effectively removeall powder deposited thereon without causing significant amounts of theresin to be removed or built up at the edges of the slots 30, which isachieved due to the absence of any wiping effect.

The shafts 32, 34 are preliminarily cleaned in the belt contact unit 124by passage over the slotted face plates 190, 190 of the vacuum blocks188, and by the contact elements 166 of the fourth set of beltassemblies, as illustrated in FIG. 11. However, it should be appreciatedthat either or both of these effects might be eliminated, with reliancebeing placed entirely upon the action in the precuring unit 204 topermit powder removal, but preferably both the contact belt unit 124 andalso the precuring unit 204 will be provided as illustrated. From theprecuring unit 204 the rotors 26 are carried to the air knife assembly270 for a final cleaning, through the oven for complete fusion, andfinally to the cooling unit for solidification of the resin.

Subsequent to the air knife assembly 270 and ahead of the oven is asecond transfer point which occurs over the rearmost drive sprocket 13.Since the transfer is quite comparable to that which occurs over thesprocket 12, a detailed explanation is not believed to be necessary.However, as illustrated in FIG. 16, the construction of the conveyor 20to which the cores are transferred at this point is somewhat differentfrom any described previously. More particularly, the conveyor 20consists of a pair of spaced chain assemblies, generally described bythe numeral 283 (only one being shown in FIG. 16) which, at the point oftransfer, lie to either side of the conveyor 18. Each of the chainassemblies 283 includes an endless sprocket chain 292 on which ismounted a multiplicity of U-shaped cradles 284. Each of the cradles 284has in its inner wall 288 an upwardly opening U-shaped socket 286 inwhich the shafts of the rotors are received. The cradles 284 have adepending flange element 290 secured thereto, and the flange elementsconstitute part of the sprocket chain 292 while affording the means ofattachment thereto. As will also be appreciated, drive sprocket 13 willconsist of a pair of sprocket wheels similar to those employed for thedrive sprocket 12, one wheel being used to support and drive each of thechain assemblies The particular fusible resin used may vary greatly;however, of the types of materials which are suitable, thermoplastics,and particularly synthetic thermoplastic resins, are preferred.Exemplary of such thermoplastic resins are the vinylidenes and vinyls(e.g., polystyrene and polyvinyl chloride), the olefins (e.g.,polyethylene, polypropylene and copolymers thereof), the cellulosics,polyamides (e.g., nylons), etc.

As will be appreciated by those skilled in the art, many changes may bemade in the illustrated apparatus without departing from the concept ofthe invention hereof. For example, heating may be by any appropriatemeans, and may employ convection, conduction, infrared, induction, orlike effects. Similarly, cooling may be accomplished in any appropriatemanner, such as by the use of cooled air or other fluid, conventionalrefrigeration, etc. The proper electrical circuitry will also be readilyapparent and of the type conventionally employed in the electrostaticcoating and electromechanical arts. It should be appreciated that,although good practice and safe operating procedures will normallydictate electrical grounding of the apparatus and of the workpiece bycontact therewith, no special provision need normally be made forgrounding of the workpiece to ensure adequate electrostatic attractionand adhesion. The high voltage charging of the particles will] usuallysuffice to establish an adequate potential relative to the workpiece,regardless of the measures taken with respect to the latter; however,independent connections may be made to the workpiece if so desired.

As used herein, the terms "partial fusion and coherence" are intended toconnote a state in which the individual particles of the resin have beenaffected by heat sufficiently to at least loosely join them together, soas to resist separation. In such a condition individual particles may bediscernible, whereas upon complete fusion or melting the particles areno longer identifiable as such. Due to the variety of resinous materialsthat may be employed in the practice of the invention, it is notpossible to place specific values upon the temperatures involved forfusion or melting without unduly limiting the scope thereof. Moreover,the conditions of operation that are appropriate in each instance willbe readily apparent to those skilled in the an in view of the foregoingdetailed information.

Thus it can be seen that the present invention provides a novel methodand apparatus for the production of a unified, adherent coating of aheat fusible resin upon a limited portion of a workpiece. Morespecifically, it provides such a method and apparatus forelectrostatically coating the workpiece and for efiecting the removal ofthe resinous material from selected portions thereof which are to beuncoated, and the method and apparatus are particularly adapted forcoating reentrant surface portions of generally cylindrical articles.The coatings are produced quickly, easily and economically, and on anautomatic and continuous basis if so desired. A novel precuring deviceis also provided which is adapted to set the coating at one zone of aworkpiece while simultaneously maintaining the particulate form of theresin at a second zone to facilitate its complete removal therefrom.

Having thus described the invention we claim:

1. In an apparatus for producing a unified, adherent coating ofheat-fusible resinous material upon only a portion of a workpiece havingproximate first and second zones in heat-conductive contact with oneanother, the combination comprising:

a. a chassis;

b. means on said chassis for producing a cloud of electrostaticallycharged solid particles of resinous material;

c. a precuring unit on said chassis including means for heating thefirst zone of the workpiece to be coated and means for simultaneouslycooling the second zone thereof; and

d. means for carrying the workpiece along a travel path through saidcloud-producing means and said precuring unit,

said heating and cooling means being so disposed as to enable heating ofthe first zone of the workpiece to a relatively high temperature aboveambient while the second zone thereof is simultaneously maintained at arelatively low temperature substantially below said relatively hightemperature, so that the workpiece may be exposed to the chargedparticles from said cloudproducing means with the workpiece chargedeffectively opposite to the particles to cause a layer thereof todeposit upon the workpiece, said heating means causing at least partialfusion and coherence of the particles at the first zone and said coolingmeans substantially preventing fusion and coherence of particles at thesecond zone thereof, removal of the particles from the second zonethereby being facilitated.

2. The apparatus of claim 1 wherein said heating and cooling meansextend along substantially the same length of said travel path, saidcooling means comprising an element having a cooled support surface uponwhich the second zone of the workpiece rests in heat transfer contactduring movement through said precuring unit.

3. The apparatus of claim 1 additionally including cleaning meanspositioned on said chassis along said travel path downstream of saidprecuring unit for effecting the removal of particles of resinousmaterial from the second zone of the workpiece.

4. The apparatus of claim 3 additionally including post heating meanspositioned along said travel path downstream of said cleaning means,said post heating means being adapted to fully heat the entire workpieceso as to melt the remaining particles of resinous material and producefrom them a unified and adherent coating on the first zone of theworkpiece.

5. The apparatus of claim 1 additionally including particle removalmeans positioned on said chassis between said cloud-producing means andsaid precuring unit to effect at least a preliminary removal ofparticles of resinous material from at least the second zone of theworkpiece.

6. The apparatus of claim 1 wherein said apparatus is particularlyadapted for producing a coating upon a generally cylindrical articlehaving a central portion providing the first zone thereof and endportions extending axially from either side of the central portiontogether providing the second zone of the article, said cooling means ofsaid precuring unit comprising two elements each having a cooled surfaceextending along an opposite side of said travel path and being adaptedto support and thereby cool one of the end portions of the articleduring movement thereof along said travel path through said unit, saidheating means comprising a heating element extending along said travelpath and lying generally between said cooled surfaces to heat thecentral portion of the article during such movement.

7. The apparatus of claim 2 wherein said cooling means additionallyincludes an overlying element having a cooled lower surface extendingsubstantially parallel and in spaced alignment over said support surfaceto provide a convective cooling effect upon the second zone of theworkpiece during passage therebeneath.

8. The apparatus of claim 7 wherein said carrying means comprises aconveyor including an upstanding element for supporting an articleextending transversely across said travel path with the first and secondzones of the article lying on opposite sides thereof, said conveyorelement cooperating with said overlying element of said cooling means toprovide a shield against heat flow by radiation and convection to thesecond zone of the article.

9. The apparatus of claim 1 wherein said precuring unit includes a baseproviding at least in part said cooling means thereof, said base havingan elongated channel extending therein along said travel path throughwhich at least a portion of the workpiece passes, the surfaces of saidbase defining said channel being cooled to provide a cooling effectpartially about said workpiece.

10. The apparatus of claim 9 wherein said heating means comprises aheating element supported by a cover member movably mounted upon saidchassis for displacement from a normal position over said travel path toa position outwardly therefrom.

11. The apparatus of claim 10 wherein said cooling means additionallyincludes an overlying element supported by said cover member and havinga cooled lower surface, with said cover in said normal position thereofsaid lower surface extending substantially parallel to and in spacedalignment over said support surface to provide a convective coolingeffect upon the second zone of the workpiece during passagetherebeelectrode means spans a lesser area than said plate to provide anelectrode-free vertical corridor within said receptacle through whichparticles of the resinous material may pass without acquiring asignificant charge, said receptacle also including a device for sensingthe level of the bed of particles therewithin to which said feed meansis responsive to convey resinous material from said reservoir to saidchamber when said bed level falls below a preselected height, saidsensing device being positioned within said vertical corridor over saidpermeable plate to minimize the effect of electrostatic charging uponthe sensed level of the bed.

14. The apparatus of claim 13 wherein said electrode is a generallyplanar, grid-like structure and is disposed adjacent the upper surfaceof said gas-permeable plate, said electrode and plate beingsubstantially coextensive except at one area of said plate over whichsaid electrode does not extend to thereby provide said electrode-freevertical corridor.

1. In an apparatus for producing a unified, adherent coating ofheat-fusible resinous material upon only a portion of a workpiece havingproximate first and second zones in heat-conductive contact with oneanother, the combination comprising: a. a chassis; b. means on saidchassis for producing a cloud of electrostatically charged solidparticles of resinous material; c. a precuring unit on said chassisincluding means for heating the first zone of the workpiece to be coatedand means for simultaneously cooling the second zone thereof; and d.means for carrying the workpiece along a travel path through saidcloud-producing means and said precuring unit, said heating and coolingmeans being so disposed as to enable heating of the first zone of theworkpiece to a relatively high temperature above ambient while thesecond zone thereof is simultaneously maintained at a relatively lowtemperature substantially below said relatively high temperature, sothat the workpiece may be exposed to the charged particles from saidcloud-producing means with the workpiece charged effectively opposite tothe paRticles to cause a layer thereof to deposit upon the workpiece,said heating means causing at least partial fusion and coherence of theparticles at the first zone and said cooling means substantiallypreventing fusion and coherence of particles at the second zone thereof,removal of the particles from the second zone thereby being facilitated.2. The apparatus of claim 1 wherein said heating and cooling meansextend along substantially the same length of said travel path, saidcooling means comprising an element having a cooled support surface uponwhich the second zone of the workpiece rests in heat transfer contactduring movement through said precuring unit.
 3. The apparatus of claim 1additionally including cleaning means positioned on said chassis alongsaid travel path downstream of said precuring unit for effecting theremoval of particles of resinous material from the second zone of theworkpiece.
 4. The apparatus of claim 3 additionally including postheating means positioned along said travel path downstream of saidcleaning means, said post heating means being adapted to fully heat theentire workpiece so as to melt the remaining particles of resinousmaterial and produce from them a unified and adherent coating on thefirst zone of the workpiece.
 5. The apparatus of claim 1 additionallyincluding particle removal means positioned on said chassis between saidcloud-producing means and said precuring unit to effect at least apreliminary removal of particles of resinous material from at least thesecond zone of the workpiece.
 6. The apparatus of claim 1 wherein saidapparatus is particularly adapted for producing a coating upon agenerally cylindrical article having a central portion providing thefirst zone thereof and end portions extending axially from either sideof the central portion together providing the second zone of thearticle, said cooling means of said precuring unit comprising twoelements each having a cooled surface extending along an opposite sideof said travel path and being adapted to support and thereby cool one ofthe end portions of the article during movement thereof along saidtravel path through said unit, said heating means comprising a heatingelement extending along said travel path and lying generally betweensaid cooled surfaces to heat the central portion of the article duringsuch movement.
 7. The apparatus of claim 2 wherein said cooling meansadditionally includes an overlying element having a cooled lower surfaceextending substantially parallel and in spaced alignment over saidsupport surface to provide a convective cooling effect upon the secondzone of the workpiece during passage therebeneath.
 8. The apparatus ofclaim 7 wherein said carrying means comprises a conveyor including anupstanding element for supporting an article extending transverselyacross said travel path with the first and second zones of the articlelying on opposite sides thereof, said conveyor element cooperating withsaid overlying element of said cooling means to provide a shield againstheat flow by radiation and convection to the second zone of the article.9. The apparatus of claim 1 wherein said precuring unit includes a baseproviding at least in part said cooling means thereof, said base havingan elongated channel extending therein along said travel path throughwhich at least a portion of the workpiece passes, the surfaces of saidbase defining said channel being cooled to provide a cooling effectpartially about said workpiece.
 10. The apparatus of claim 9 whereinsaid heating means comprises a heating element supported by a covermember movably mounted upon said chassis for displacement from a normalposition over said travel path to a position outwardly therefrom. 11.The apparatus of claim 10 wherein said cooling means additionallyincludes an overlying element supported by said cover member and havinga cooled lower surface, with said cover in said normal position thereofsaid lower surface extending substanTially parallel to and in spacedalignment over said support surface to provide a convective coolingeffect upon the second zone of the workpiece during passagetherebeneath.
 12. The apparatus of claim 1 wherein said cloud-producingmeans includes an electrostatic cloud chamber, said chamber comprising areceptacle having means for producing a fluidized bed of chargedparticles including a gas-permeable plate extending thereacross in agenerally horizontal intermediate plane spaced above the bottom wallthereof to define a plenum chamber therebelow and having electrode meansextending thereacross for electrostatically charging particles of solidresinous material passing proximate thereto.
 13. The apparatus of claim12 additionally including a particulate material reservoir having feedmeans communicating with said cloud chamber, wherein said electrodemeans spans a lesser area than said plate to provide an electrode-freevertical corridor within said receptacle through which particles of theresinous material may pass without acquiring a significant charge, saidreceptacle also including a device for sensing the level of the bed ofparticles therewithin to which said feed means is responsive to conveyresinous material from said reservoir to said chamber when said bedlevel falls below a preselected height, said sensing device beingpositioned within said vertical corridor over said permeable plate tominimize the effect of electrostatic charging upon the sensed level ofthe bed.
 14. The apparatus of claim 13 wherein said electrode is agenerally planar, grid-like structure and is disposed adjacent the uppersurface of said gas-permeable plate, said electrode and plate beingsubstantially coextensive except at one area of said plate over whichsaid electrode does not extend to thereby provide said electrode-freevertical corridor.